In the manufacture of multilayer ceramic (MLC) substrates for integrated circuit semiconductor package structures, a plurality of green ceramic sheets are formed by doctor blading a slurry containing a resin binder, a particulate ceramic material, solvents, and a plasticizer, drying the doctor bladed sheet and cutting it into appropriate size sheets. Via holes are then punched for forming electrical interconnections through the sheet, electrically conductive paste is deposited in the holes and in appropriate patterns on the surface of the sheets, the sheets stacked and subsequently fired at a sintering temperature. Punching of via holes in ceramic sheets presents formidable engineering problems in view of their small size and density. It is conventional to punch via holes with apparatus of the type disclosed in IBM TDB Vol. 13 No. 4 Feb. 1971 P. 2536 or IBM TDB Vol. 16 No. 12 May 1974 P. 3933. In these apparatus a plurality of punch elements arranged in the grid are indexed over the green sheet which is covered by an interposer mask. The interposer mask contains openings where holes are desired to be punched. When the punch elements contact the interposer mask as the punch head is moved downwardly, a hole will be punched where the openings occur since the punch element will pass through the openings in the interposer mask, and through the ceramic green sheet. In other areas covered by the interposer mask, i.e., where holes are not desired, the interposer mask will cause the punch element to be retracted into the head.
Automated punch apparatus which utilize individually programmable punches have been suggested in IBM TDB Vol. 20 No. 4 Sept. 1977 P. 1379. This type of punching apparatus does not require the aforedescribed interposer mask, since the individual punching elements can be activated electrically upon command.